Ricciardo's Renault slowest in F1 testing

Australian Daniel Ricciardo was slowest around the Circuit de Catalunya on his first day of Formula One testing in his new Renault.

Daniel Ricciardo was happy to have put in 44 laps in his new Renault during F! testing in Barcelona. (AAP)

Renault's Daniel Ricciardo admits he is still learning his new Formula One car after the Australian was slowest in testing at the Circuit de Catalunya.

The Australian, who joined Renault from Red Bull at the end of last year, and his teammate Nico Hulkenberg were 11th and 10th fastest on Monday, almost three seconds slower than Ferrari's Sebastian Vettel.

Having sat out the first half of the day, Ricciardo got in 44 laps with a best time of 1min 20.983sec.

"It's a good feeling to be behind the wheel of a Formula One car again after a long winter waiting,'' Ricciardo told The Herald Sun.

"Today was about bedding ourselves back into it and, for me, continuing to learn about a new car and a new team.

"It was a decent afternoon and it's important we keep increasing our mileage.

"We have plenty to analyse but it's been a promising first official day."

Four-times world champion Vettel said he could not have hoped for a better day after he was fastest with a time of 1:18.161 and put in 169 laps, more than any of the 11 drivers.

"Unbelievable," Vettel told reporters.

"The car was working really well, we had no issues slowing us down. We actually completed the programme just the way we wanted."

McLaren's Carlos Sainz, stepping into the shoes of departed compatriot Fernando Alonso, was the only driver other than Vettel to break the 1.19 barrier.

Five-times world champion Lewis Hamilton shared the work at Mercedes with teammate Valtteri Bottas, who did the morning session.

Bottas was eighth fastest with Hamilton ninth, the pair completing 150 laps between them on harder tyres than the Ferrari.

Red Bull, now powered by Honda after their split from Renault, managed 128 laps with Dutch driver Max Verstappen in action and fourth fastest.

Alfa Romeo, the renamed former Sauber team, were fifth fastest with Kimi Raikkonen at the wheel.

Only nine of the 10 teams appeared on track, with struggling Williams failing to get their car ready on time and not expecting to test until Wednesday at the earliest.

Testing continues until Thursday and resumes on February 26 before the season's first race at the Australian Grand Prix on March 17.